This application is based on and claims the priority under 35 U.S.C. xc2xa7 119 of German Patent Application 198 54 741.2, filed on Nov. 27, 1998 the entire disclosure of which is incorporated herein by reference.
The invention relates to a wedge element for attachment to a bottom surface of an aircraft wing directly along the trailing edge of the wing whereby the wedge element referred to herein as edge wedge preferably extends in parallel to the trailing edge of the wing.
U.S. Pat. No. 4,542,868 (Boyd) discloses a wedge-shaped structural component for attachment to the bottom surface of an aircraft wing profile near or along the trailing edge of the aircraft wing. The purpose of such a conventional wedge shaped structural component is to improve the lift coefficient and to reduce the drag during cruising speeds. The conventional wedge-shaped component has a downward height within the range of 0.5% to 1.5% of the local chord of the aircraft wing. The downwardly facing or outer surface of the conventional wedge component encloses with the chord an angle within the range of 15xc2x0 to 45xc2x0. The conventional wedge component is secured directly along the wing trailing edge or at a distance from the wing trailing edge whereby the distance corresponds up to 1% of the length of the local wing chord. While the conventional wedge component improves the lift coefficient and reduces the drag during cruising flight, it does not provide any compensation for unavoidable structural tolerances and related asymmetric characteristics of the aircraft.
An other publication xe2x80x9cJane""s All The World""s Aircraftxe2x80x9d published in Jane""s Yearbooks 1976-77 edition, discloses on pages 31 and 81 single engine propeller aircraft equipped with wings having ailerons secured to the trailing edge of the wing and provided with bail edges. These bail edges on the ailerons are arranged only on one side of the aircraft and produce a counter moment to the rolling moment which is produced by the propeller wake of a single engine aircraft. Asymmetric aircraft characteristics caused by unavoidable structural tolerances are not compensated by such bail edges on the ailerons.
U.S. Pat. No. 4,867,396 (Wainfan) discloses a micro flap trailing edge device for an aircraft wing for improving the lift coefficient and for reducing drag. The flap is a flat plate-like member having a length within the range of about 0.5% to 1.5% of the local chord of the aircraft wing. The plate-like flap forms an angle with the wing chord within the range of 5xc2x0 to 25xc2x0. The purpose of such a micro flap attached to the wing downstream of the trailing edge of the wing is to improve lift without any compensation for aircraft asymmetric characteristics that are due to unavoidable structural tolerances.
In view of the forgoing it is the aim of the invention to achieve the following objects singly or in combination:
to provide an edge wedge for use in combination with an aircraft wing, particularly only with one of the two wings, whereby the edge wedge is so constructed that any asymmetric aircraft characteristics that are due to the sum of all unavoidable structural tolerances are compensated;
to combine an aircraft wing with an edge wedge, specifically an edge wedge that will counteract aircraft asymmetric characteristics including asymmetric flight characteristics;
to advantageously influence the pressure distribution on the upper surface and the bottom surface of an aircraft wing;
to cause a localized increase of lift on an aircraft wing which compensates for asymmetrical aircraft characteristics by generating a desirable counter rolling moment; and
to select the desired counter-rolling moment by correspondingly selecting the width of the compensating edge wedge in the direction of the wing span width or wing length.
According to the invention the above objects have been achieved by a trailing edge wedge for an aircraft wing which edge wedge is constructed for attachment to the bottom surface of the aircraft wing directly next to and along the trailing edge of the wing and preferably parallel thereto. The edge wedge has a triangular cross-section in a longitudinal chord axis direction of the aircraft wing and points with its wedge tip toward the leading wing edge. The edge wedge has an inner surface for connection directly to the bottom surface of the aircraft wing, an outer edge wedge surface facing downwardly and an end surface facing rearwardly. The outer edge wedge surface has a length in the longitudinal chord direction. When the edge wedge is attached to the bottom wing surface, the trailing wedge end surface is preferably flush with the trailing edge of the wing or within 0.5% of the local wing chord. The inner edge wedge surface that faces the bottom wing surface for connection to the bottom wing surface and the outer edge wedge surface facing away from the wing enclose a wedge angle xcex1 within the range of about 5xc2x0 to about 20xc2x0. The angle xcex1 is preferably within the range of 5xc2x0 to less than 17xc2x0. Preferably the edge wedge is attached to only one wing of the aircraft for compensating asymmetric aircraft characteristics.
According to the invention there is further provided a combination of an aircraft wing with the present edge wedge. In the combination the inner edge wedge surface is secured directly to the bottom wing surface along the trailing edge of the wing so that the inner edge wedge surface and the bottom wing surface are flush with each other. Moreover, the rearwardly facing wing trailing edge surface and the back end wedge surface of the trailing edge extend preferably in the same plane or within 0.5% of the local wing chord.
In one embodiment of the invention the wedge angle xcex1 enclosed by the inner and outer wedge surfaces is equal to the flow-off angle of the wing. In another embodiment the wedge angle differs from the flow-off angle. Preferably the flow-off angle is larger than the wedge angle. Further, in a preferred embodiment the edge wedge length in the direction of the chord axis of the wing is about 1% of the length of the local wing chord. The rearwardly facing back end wedge surface wedge is preferably directly connected to the trailing edge of the wing or within 0.5% of local wing chord and has a height (h) of about 0.1% to 0.3% of the local wing chord.
In the embodiment of the invention, in which the flow-off angle differs from the wedge angle, the outer surface of the edge wedge is curved downwardly whereby the flow-off angle becomes larger than the wedge angle. The flow-off angle may be within the range of up to 60xc2x0.
The present edge wedge advantageously influences the pressure distribution on the upper wing surface and the bottom wing surface where the edge wedge is secured to bottom surface of the wing. The present edge wedge functions as a divergent trailing edge of the wing whereby a desirable localized lift increase is achieved which in turn causes a desired counter rolling moment for compensating any asymmetric characteristics of the aircraft or of its flight. Another advantage of the invention is seen in that the desired rolling moment or rather counter-rolling moment can be selected by varying the width of the edge wedge in the direction of the span width or length of the wing to which the edge wedge is attached. Thus, the present edge wedge provides a flexible means for an advantageous compensation not only of asymmetrical characteristics of the aircraft itself that are due to unavoidable structural tolerances but also compensates for asymmetric flight characteristics that may occur unintentionally particularly during cruising flight of an aircraft. The wedge width in the wing span direction is selected according to the desired counter rolling moment.